Cement compositions, such as cement pastes prepared by mixing cement, water, and other additives, mortar prepared by adding sand to the cement paste, and concrete prepared by further adding large aggregates such as gravel to the mortar and mixing the resulting mortar, are used in large amounts in a variety of construction materials and the like. However, the prepared cement composition starts to harden over time due to hydration reaction between cement and water and thus workability thereof is gradually deteriorated. In this case, water is additionally added to enhance workability and, consequently, compression strength is reduced and cracks in the cement composition occur and thus a total amount of water used in a cement composition is limited. Thus, a variety of cement additives for reducing the amount of water and maintaining dispersibility of a cement composition have been developed.
In particular, among such cement compositions, concrete requires completion of all tasks, ranging from concrete mixing to concrete pouring, within a short period of time because slump reduction generally occurs after 30 minutes. Recently, there has been a need to develop a cement additive that meets demand for increasing unit number according to reduction in quality of concrete aggregates, has higher water-reducing performance than conventional plasticizers due to use of mechanized modem equipment and traffic congestion, or has excellent slump retaining performance.
To increase fluidity of cement compositions, various kinds of cement dispersants are currently used. However, in general, when a hydraulic composition with high water reduction performance is prepared using a cement dispersant, slump loss is significant and workability and constructability are deteriorated. Thus, to prevent slump loss, efforts to use a water-soluble polycarboxylic copolymer with slump loss prevention performance as a cement dispersant are conventionally made. Examples of the water-soluble polycarboxylic copolymer include, but are not limited to, water-soluble vinyl copolymers prepared through copolymerization of methacrylates (disclosed in Japanese Patent Application Laid-open No. Hei 1-226757, U.S. Pat. No. 4,962,173, and Japanese Patent Application Laid-open No. Hei 4-209613) and copolymers of maleic anhydride and alkenyl ether or derivatives thereof (disclosed in Japanese Patent Application Announcement No. Sho 58-38380, Japanese Patent Application Laid-open No. Sho 63-285140, and Japanese Patent Application Laid-open No. Hei 2-163108). However, in conventional methods of using the water-soluble copolymer as a cement dispersant, slump loss is insufficiently prevented.
In addition, to prevent such slump loss, use of a fluidity reduction inhibitor and a cement dispersant in combination has been proposed. As an example, a method of obtaining slump loss prevention using a non-water-soluble copolymer obtained from maleic anhydride and olefin and a cement dispersant in combination and using characteristics in which the non-water-soluble copolymer is hydrolyzed by a basic hydroxide produced by hydration of cement to slowly become a water-soluble copolymer is proposed (Japanese Patent Application Announcement No. Hei 5-67579). However, in the conventional method of using a fluidity reduction inhibitor and a cement dispersant in combination, slump loss prevention performance is changed and deteriorated over time and condensation delay is large.
Meanwhile, Japanese Patent Application Laid-open No. Hei 7-267705 discloses a cement dispersant including three kinds of polymer. The three kinds of polymer include a copolymer (a first component) of a polyalkylene glycol mono(meth)acrylate compound and a (meth)acrylic acid compound, a copolymer (a second component) of a polyalkylene glycol mono(meth)allyl ether compound and maleic anhydride, and a copolymer (a third component) of a polyalkylene glycol mono(meth)allyl ether compound and a maleic acid-esterified polyalkylene glycol compound. The cited patent specification describes that, when used alone, the first component increases the initial fluidity of cement but is poor in slump-retaining ability and increases the viscosity of the cement composition. In addition, the cited patent specification describes that, when used alone, the second component requires time to increase initial fluidity and, even when the initial fluidity is increased by increasing the amount thereof, it causes phase separation of the cement composition over time. In addition, the cited patent specification describes that, when used alone, the third component is further poor in dispersibility of the cement composition and that, therefore, such effects that cannot be obtained by use of each of the three components alone are produced by using the three components in combination in a particular mix ratio. Thus, it is presumed in the cited specification that differences in action mechanisms among the three components in the cement composition are due to molecular weight of each component and differences in initial fluidity increasing effects are due to a faster adsorption rate on cement particles of a (meth)acrylic acid-based functional group-containing polymer than a maleic acid-based functional group-containing polymer, whereby the latter exhibits higher initial fluidity. In addition, it is further described that a component higher in rate of adsorption is poor in the ability to retain fluidity.
At present, a technique is known in the art which includes use of a polyalkylene glycol mono(meth)acrylate/(meth)acrylic acid copolymer and an unsaturated polyalkylene glycol monoalkenyl ether/maleic acid copolymer in combination. However, cement compositions having both sufficient initial dispersibility and slump retaining ability have not yet been disclosed and addition of a dispersant in a large amount is needed to exhibit sufficient initial dispersibility. In particular, it is further difficult to select an additive that imparts sufficient dispersibility and dispersion retaining ability to cement in a high water reducing ratio range.
Therefore, there is an urgent need to develop technology for fundamentally addressing these problems.